高温对玄武质凝灰岩力学性能的影响及其机理分析

Effects of high temperatures on mechanical performance of basaltic tuff and mechanism analysis

研究选取四川得荣县的玄武质凝灰岩为研究对象,按照固定围压200 MPa,实验温度为200℃～800℃开展高温高压实验,取得7个样品的实验数据。通过对实验数据的分析可知,在围压一定,实验温度不断升高的条件下,岩样的弹性模量和屈服强度都不断降低,当实验温度达到700℃,岩样变形主要以流变为主。实验温度400℃是岩样力学性质发生显著变化的临界温度。通过对实验后样品的成份分析可知,当实验温度超过400℃后,岩样中的黏土矿物含量随着温度的升高而降低,而斜长石和方解石的含量在不断升高,当温度超过500℃以后,岩样中出现了新的矿物——橄榄石;岩样的电镜扫描结果显示,在400℃之前,岩样内基本没有明显的微裂隙,但是当温度达到700℃和800℃时,岩样内出现明显的部分熔融现象,温度越高,部分熔融现象越明显,而且在800℃时,出现明显的矿物重结晶现象。微观的结构及成份的变化导致了宏观的物理力学性能的显著变化。本次实验研究结论与前人研究成果较为一致,但是从物质成份和样品微结构方面对岩石力学性能对高温响应的机理进行了初步解释。

The basaltic tuff from Derong County, Sichuan Province, is selected for the tests with a high confining pressure of 200 MPa and temperatures from 200 to 800℃. The test results of 7 specimens are obtained and show that the Young＇s modulus and yield strength of the rock specimens decrease when the test temperature rises and the confining pressure is constant. When the test temperature reaches 700℃, the major failure mode of the rock specimens is rheology. The test temperature of 400℃ is the critical temperature for remarkable charge of the mechanical performance of the rock specimens. The results of X-ray dissipation analysis indicate that the mineral contents of the clay in the test specimen decrease as the temperature rises and exceeds 400℃, but the plagioclase and calcite contents increase. When the temperature exceeds 500℃, a new mineral, olivine, appears in the rock specimen. The SEM photos of the rock specimens show that before 400℃, it is very difficult to find out micro fractures in the rock specimens, but when the test temperature reaches 700℃ and 800℃, the partial melting phenomenon occurs in the rock specimens, at the same time, when the test temperature reaches 800℃, the recrystallization phenomenon occurs. The macro mechanical performance of the rock specimens corresponds very well to the change of micro textures and mineral contents. The research findings agree with the others and give some explanations for the response mechanism of the mechanical performance of rock specimens under high temperatures and high confining pressures from the view point of micro texture and ingredient.